Journal of Accident Investigation

MATTHEW R. FOX, CARL R. SCHULTHEISZ, JAMES R. REEDER, AND BRIAN J. JENSEN
Figure 12. Comparison of aft lugs from the accident vertical stabilizer and subsequent subcomponent tests. In each photo, the small, unlabeled arrows
indicate where translaminar cracks or fractures intersected the outboard surfaces of the lugs, and a large, unlabeled arrow indicates loading direction (the
force vector for the horizontal and vertical loading components for each lug). The lugs from the first and second tests were left aft lugs, and as such, the
orientations are mirror images of the accident right aft lug and the third test lug.
loading conditions, fracture of the vertical stabilizer would
have initiated at the right aft lug. Accordingly, three aft lugs
were obtained for mechanical testing under applied loads that
matched those that were derived from recorded flight accident
data. The lug for the first test was obtained from a production
left skin panel from which sections were cut for destructive
testing, while the aft lug was not disturbed. Lugs for the second
and third tests were obtained from a vertical stabilizer that had
been removed from service after experiencing loads exceeding
design limit loads. The three lug specimens were tested at
Airbus under Safety Board supervision in a loading fixture that
applied the prescribed forces and moments to the lugs. Testing
of each lug continued until a load change associated with a
translaminar fracture or crack was observed. Fracture loads for
these three tests were consistent with calculated accident loads
and with earlier tests completed by Airbus during certification. 19
19 (a) National Transportation Safety Board, Structures Group Factual
Report Addendum 17, NTSB Public Docket, 2004; (b) National
Transportation Safety Board, Structures Group Factual Report
Addendum 16, NTSB Public Docket, 2004; (c) National Transportation
Safety Board, Structures Group Factual Report Addendum 1 , NTSB
Public Docket, 2004; (d) National Transportation Safety Board,
Structures Group Factual Report Addendum 8C, NTSB Public Docket,
2004; (e) National Transportation Safety Board, Structures Group
Factual Report Addendum 6 (Rev A), NTSB Public Docket, 2004.
A fractographic examination of each lug was conducted after
completing the tests, as documented by the Safety Board. 20
Before being tested, each lug was examined for non-visible
defects or damage using ultrasonic inspection. 21 No defects
were observed in the first test lug. Some damage was detected
in the second and third test lugs near the lug attachment
hole and in some areas, in the lug fitting assembly transition
area above the lowermost rib, but these lugs had experienced
in-service loads exceeding design limit loads. Following the
tests, the lugs were examined again using ultrasonic inspection,
which showed that the preexisting damage in these lugs grew in
size during the testing. Overall views of the lugs from each test
are shown in figure 12 (outboard surface view).
Results from the fractographic examination showed that
the test lugs fractured at locations similar to those on the
accident right aft lug. In test 1, loading was interrupted after
a translaminar crack occurred at the location indicated by
the large arrow in the upper right photo in figure 12. The
translaminar fracture was located on the forward part of the
20 National Transportation Safety Board, Materials Laboratory Factual
Report 04-06 , NTSB Public Docket, 2004.
21 National Transportation Safety Board, Materials Laboratory Factual
Report 04-06 , NTSB Public Docket, 2004.
20 NTSB JOURNAL OF ACCIDENT INVESTIGATION, SPRING 2006; VOLUME 2, ISSUE 1